A little fresh air is good for your health, or so the saying goes. Culturally, the association of fresh air with healthiness dates back centuries. Whether its by the sea or in the country, research is certainly being outside in green space comes with both psychological and physiological benefits.

But, is country air better than city air? And if so, why? Mike Moore, an environmental toxicologist at the University of Exeter in the U.K., has a theory. In an opinion piece in New Scientist, Moore proposes that country air’s healthfulness might actually derive from some of its more toxic qualities. (He also lays out this hypothesis in paper in the July issue of Environmental Research.)

The theory goes like this: Urban areas have higher air pollution rates, but plants, fungi and microbes contribute to air quality, too. All of these organisms produce airborne chemicals—sometimes to defend themselves from threats, sometimes to attract mates or pollinators.

“The presence of these biomolecules in the atmosphere represents a radical departure from the urban environment, which is more likely to contain synthetic pollutants and mildew,” writes Moore in New Scientist.

In particular, plants, algae and cyanobacteria produce compounds called phytochemicals. While many of these chemicals might be poisonous to a predator, modern humans can probably tolerate them at low doses—because of our exposure over millennia, according to Moore. In fact, he thinks inhaling these “biogenic” compounds may influence a specific communication pathway between our cells for the better.

While it sounds a bit out there, Moore might be onto something. Studies suggest that consuming some phytochemicals though plants in our diet blocks the activity of a protein that can overactivate cell growth. Switching this protein signal off suppresses tumors and destroys damaged cells. As Moore explains, since eating these compounds seems to be good for us, it follows that breathing them in could be beneficial, as well.